How to use MVVM pattern on Android Radosław Piekarz 

#droidconKrakow #RoboBinding 

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Android everyday basis this.addButton = (Button) findViewById(R.id.button); this.addButton.setOnClickListener(new View.OnClickListener(){ @Override public void onClick(View v) { //do something cool } }); 

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Butterknife public class MyActivity extends Activity { @InjectView(R.id.button) Button button; //…... @OnClick(R.id.button) void onButtonClicked() { //change the world //or maybe change the UI } // } 

Android Annotations @EActivity(R.layout.main_activity) public class MyActivity extends Activity { @ViewById(R.id.button) Button button; @Click(R.id.button) public void onButtonClicked() { //change the world //or maybe change the UI } } 

Is it enough? 

Is it enough? NO! 

Model View Presenter ● The model is an interface defining the data to be displayed ● The view is a passive interface that displays data (the model) and routes user commands (events) to the presenter to act upon that data. ● The presenter acts upon the model and the view. It retrieves data from repositories (the model), and formats it for display in the view. 

Model View Presenter on Android #1 public interface MyView { void hideLoading(); void showLoading(); void renderItems(final Collection items); boolean isReady(); boolean isAlreadyLoaded(); } 

Model View Presenter on Android #2 public class MyViewPresenter extends Presenter { private MyView view; public void setView(MyView view) { //checking if view is not null etc... this.view = view; } @Override public void initialize() { if(view.isAlreadyLoaded()) { view.showLoading(); } } 

Say hello to Model-View-ViewModel 

Model-View-ViewModel ● The Model, which provides a view-independent representation of your business entities. ● The View class which is the user interface. It displays information to the user and fires events in response to user interactions. ● The ViewModel class, which is the bridge between the view and the model. Each View class has a corresponding ViewModel class. 

MVVM on Android #1 public class MyFragmentViewModel { private Listener listener; public void initialize() { listener.onVisibilityFlagChanged(true); } public void setListener(Listener listener) { this.listener = listener; } public interface Listener { void onVisibilityFlagChanged(final boolean visible); } } 

MVVM on Android #2 public class MyFragment extends BaseFragment implements MyFragmentViewModel.Listener { MyFragmentViewModel myFragmentViewModel; @Override public void onViewCreated(View view, Bundle savedInstanceState) { super.onViewCreated(view, savedInstanceState); bindViewModel(); } private void bindViewModel() { myFragmentViewModel.setListener(this); myFragmentViewModel.initialize(); } @Override public void onVisibilityFlagChanged(boolean visible) { // do some magic 

BUT CAN BE BETTER! 

MVVM on Android #3 ● https://github.com/RoboBinding ● https://github.com/gueei/AndroidBinding ● https://github.com/kejunxia/Android-Mvvm honorable mention: https://github.com/MvvmCross/MvvmCross (Xamarin) 

Why RoboBinding? ● Still developed and maintained ● +400 stars at GitHub ● Easy to use and extend ● Annotation processing and code generation 

Robobinding history ● Created in 2011 by Robert Taylor & Cheng Wei ● Added code generation in version 0.8.9 in October 2014 

RoboBinding - setup #1 buildscript { repositories { jcenter() mavenCentral() maven() { url 'https://oss.sonatype.org/content/repositories/snapshots' } } dependencies { classpath 'com.android.tools.build:gradle:0.14.2' classpath 'com.neenbedankt.gradle.plugins:android-apt:1.4' // NOTE: Do not place your application dependencies here; they belong // in the individual module build.gradle files } 

RoboBinding - setup #2 apply plugin: 'com.android.application' apply plugin: 'com.neenbedankt.android-apt' apt("org.robobinding:codegen:$robobindingVersion") { exclude group: 'com.google.android', module: 'android' } compile("org.robobinding:robobinding:$robobindingVersion") { exclude group: 'com.google.android', module: 'android' } 

Android & RoboBinding - hello world @PresentationModel public class MainViewViewModel implements HasPresentationModelChangeSupport { private PresentationModelChangeSupport changeSupport; private String name; public MainViewViewModel() { changeSupport = new PresentationModelChangeSupport(this); } public String getHello() { return name + ": hello Android MVVM(Presentation Model)!"; } public String getName()..... public void setName(String name) …. public void sayHello() { changeSupport.firePropertyChange("hello"); } @Override public PresentationModelChangeSupport getPresentationModelChangeSupport() { return changeSupport; } } 

Android meets MVVM - hello world public class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); MainViewViewModel presentationModel = new MainViewViewModel(); View rootView = Binders.inflateAndBindWithoutPreInitializingViews(this, R.layout.activity_main, presentationModel); setContentView(rootView); } } 

Android meets MVVM - hello world 

ListView, GridView and co. @ItemPresentationModel(value=StringItemPresentationModel.class) public List getItems() { //return some items.. } 

ListView, GridView and co. #2 public class StringItemPresentationModel implements ItemPresentationModel { private String value; @Override public void updateData(String bean, ItemContext itemContext) { value = bean; } public String getValue() { return value; } } 

Custom views ● No problem at all! ● Create custom binding or add dynamic binding 

Adding new bindings ● Just implement PropertyViewAttribute or TwoWayPropertyViewAttribute interface if needed ● Create binding by implementing ViewBinding interface and map PropertyView classes to the binding name ● Register binding 

Unit tests ● Our ViewModel is separated from UI Android dependencies so we create unit test without any problems @Test public void testShouldNotFail() { this.presentationModel.setA("2.0"); this.presentationModel.setB(1.5); assertEquals(expectedValue, this.presentationModel.getResult()); } 

Demo time! 

RoboBinding Pros ● minimize boilerplate code ● easy to use ● easy to extend ● fast ● pure POJO ViewModels = easy unit tests Cons ● still not everything is supported (ListView with multiple item layouts, RecycleView) 

Q&A Thank you for your attention! radzio RadoslawPiekarz { }